Fire-resistant structural body supporting metal bar for protection of water pipe

ABSTRACT

A support fitting for the heat-resistant block to protect boiler tubes, which protrudes upward at a right angle from the surface of the rib between two boiler tubes, and which is welded on the rib and has a catch to engage with the heat-resistant block on the end. The support fitting is provided with a welding surface to be welded on the rib and shaped narrower by chamfering, and a single globule of a deoxidizing conductive material used as flux is attached to the narrowed welding surface, and is a vertical piece or rod which extends a fixed distance perpendicular from the rib. The support fitting includes a first upper surface being kept horizontal to support a ferrule, which can tightly engage with the ferrule for arc stud welding, thereby the ferrule can shield the welding surface, and a second upper surface which engages with the heat-resistant block.

TECHNICAL FIELD

This invention concerns support fittings for supporting a heat-resistantassembly to protect boiler tubes which is mounted on an array of tubesbelonging to a heat exchanger (or boiler) of a heat recovery boiler in awaste incinerator or a thermal power plant. More specifically, itconcerns the support fittings for supporting a heat-resistant assemblyto protect boiler tubes. The heat-resistant assembly is used on theheating side of the tubes facing the incinerator to protect the array ofboiler tubes which constitute the plant's heat exchanger (i.e., boiler).This invention also concerns the array of boiler tubes on which thefittings are used.

TECHNICAL BACKGROUND

FIGS. 4 and 5 show a combined structure of boiler tubes andheat-resistant assembly. 10 is an array of boiler tubes in aheat-recovery boiler. A number of cylindrical tubes which constituteboiler tubes 11 are arranged in parallel. Each two of the cylindricaltubes are fixed in place by the flat rib 12. In the center of each ofthe ribs 12 is welded a support fitting 100, which is orientedvertically.

Support fittings 100 consist of a parallelogram with a vertical surface100 a, which is welded to flat rib 12, and an oblique upper surface 100b, which will engage in a heat-resistant catch 19. Generally, thevertical surface 100 a is first placed in contact with the flat rib 12,and then side foot portion 100 c is welded by hand. 16 is theheat-resistant block. The tube assembly 10, consisting of the boilertubes 11 and the flat ribs 12, must be protected from the heat andcorrosive atmosphere of the exhaust gases from combustion. As can beseen in FIG. 4, tube assembly 10 is enclosed in such a way that a 180°portion on the bottom of each tube is entirely covered. Each two leadtubes, paired in the axial direction, are protected by a block whosecross section resembles two semicircular tubes joined by a flat ribsurface 16 b. This block extends for a given length along thelongitudinal axis of the tubes. The block surrounds boiler tube assembly10 and is fitted close to but not directly against it, with a specifiedgap left between the block and the tube assembly.

19 is a heat-resistant catch by which the heat-resistant block 16 isattached through the support fitting 100 to boiler tube assembly 10 insuch a way as to be integral with the assembly. It is a rectangularprojection from the surface of flat rib 16 b in the heat-resistant block16. To insure that it has sufficient strength in the axial direction,the heat-resistant catch 19 should be no more than one third of thelength of heat-resistant block 16. The catch can be attached to theheat-resistant block in not only one place, but more than two places.

The heat-resistant block 16 and the heat-resistant catch 19 are formedby molding a material like SiC which has relatively good thermalconductivity.

A thin layer of mortar 14 is packed on the inner side of theheat-resistant block 16 and the catch 19 to enhance the cooling effectof the block 16.

The boiler tube assembly 10 and the heat-resistant block 16 configuredas described can be securely joined by means of support fitting 100 andheat-resistant catch 19. According to the prior art, the support fitting100 was hand-welded to the flat rib 12 which connects two boiler tubes11.

Because there are normally two semicircular boiler tube sections 11 inthe location where the two facing surfaces must be hand-welded, thespace into which the welding jig must be inserted is very small. Inother words, the surfaces of the two boiler tube sections 11 interferewith the welding, making the welding task difficult and extremelytime-consuming.

We therefore investigated the possibility of employing the comparativelysimple procedure of stud welding instead of the hand welding. However,with both the arc and percussion stud welding, there were problems dueto the non-rectangle shape of the support fitting 100 which made studwelding very difficult to perform.

Furthermore, the support fitting 100 does not have a round cross sectionlike the stud bolt used in the prior art, but is tall and thin. It isdifficult to achieve either the pressure or the temperature needed toweld it properly. When the long narrow fittings are to be stud-welded,they are frequently arc stud welded using a ferrule. To maintain thetemperature for two-surface arc welding, a heat-resistant porcelainferrule must be put on the end of the stud, and the welding must beexecuted while the periphery of the stud is covered by the ferrule.

The principle of arc stud welding using a ferrule can be explainedsimply with reference to FIG. 6. Ferrule 20 is placed on the end of stud110. The end of stud 110 is placed in direct contact with a base metal.When the welder pulls the trigger of the welding electrode, a currentflows between the stud 110 and the base metal 112.

The lifting mechanism 111 of the welding electrode automatically pullsup the stud 110. Inside the ferrule 20, an arc 113 is generated betweenthe stud 110 and the base metal 112 as indicated by the arrows. The arc113 is maintained for a period determined by a timer. The stud 110 andthe base metal 112 fuse, and after a given period of time, the stud 110is pressed against the base metal 112 and the current is cut off.

With this technology, then, a deoxidizing conductive material 115 asflux which is attached to the end of stud 110 by various methods acts onthe metals in such a way as to result in a welded portion 114. Theferrule 20 mainly serves as a mold for the molten metals. When thewelding is completed, it is removed as needed by a means such asbreaking it.

However, when the support fitting 100 is welded by arc stud weldingusing a ferrule, the ferrule 20 cannot completely seal the weldingsurfaces of the materials as shown in FIG. 5(B), so it cannot serve as amold.

Since support fitting 100 is to engage with the heat-resistant catch 19,it must have a stopper on its upper surface. This is why the surfacewhich is to engage with the catch 19 slants upward. When the ferrule 20is inserted onto the support fitting, as can be seen in FIG. 5(B), theupper surface of the fitting 100 is not perpendicular to the weldingsurface of the base metal (i.e., it is not horizontal). The ferrule 20,will be also oriented obliquely, so that its lower portion is not flushagainst the welding surface, making it difficult to maintain a uniformtemperature.

Because the fitting 100 is long and narrow, it will be extremelydifficult to insure that its contact with the base metal at the weldingsurface is uniform. If the arc is started from the lower end or theupper end where a considerable contact pressure is provided, a lopsidedweld may result.

SUMMARY OF THE INVENTION

In view of the problems described above, the objective of this inventionis to provide a support fitting for a heat-resistant block to protectboiler tubes which can be easily and reliably stud-welded without losingany of its function as a support fitting.

This invention concerns a support fitting for the heat-resistant blockto protect boiler tubes, which protrudes upward at a right angle fromthe surface of the rib between two boiler tubes. The support fitting iswelded on the rib and it has a catch to engage with the heat-resistantblock on its end.

The support fitting according to this invention is distinguished by thefact that the welding surface of the support fitting to the rib isshaped narrower, and by the fact that a single globule of a deoxidizingconductive material used as flux is attached to the narrowed weldingsurface.

With this embodiment of the invention, even though the shape of thesupport fitting is long and narrow, the fact that its welding surface isnarrowed makes it easier to achieve uniform contact with the base metaland increases the contact pressure on the welding surface. And becausethe deoxidizing conductive material used as flux is stuck to theconstricted welding surface in a single globule, the arc can be startedfrom the globule so that there is no possibility of a lopsided weld.

Because the constricted area is fused in its current state during arcstud welding, there is no possibility that this portion will beundercut. In other words, the surface should be constricted so that itcannot be undercut.

Because the welding surface is constricted, the fused portion will notextend very much beyond the periphery of the support fitting. Thus theferrule placed on that periphery will not become trapped in the moltenmetal.

This invention, then, makes it possible to use arc stud welding using aferrule easily and reliably without sacrificing the function of thesupport fitting.

In another preferred embodiment of this invention, if the supportfitting is a vertical piece which extends a fixed distance perpendicularfrom the rib, the first upper surface of the perpendicular supportfitting, which supports the ferrule, is kept horizontal, and the secondupper surface of the perpendicular support fitting, which engages withthe heat-resistant block on its end, is angled slightly upwards. Thefirst upper surface is provided with a horizontal portion which cantightly engage with the ferrule for arc stud welding.

With this configuration, when the support fitting 100 is arc stud weldedto the base metal, the first upper surface of the support fitting whichsupports ferrule 20 makes a right angle (i.e., it is horizontal) withrespect to the welding surface of the base metal. This results in theferrule also supported parallel to the welding surface of the basemetal. In other words, the entire surface of the ferrule is flushagainst the surface of flat rib 12 (the base metal) without any gap atits lower end. This facilitates maintaining a uniform temperature. Theferrule completely seals the welding surface of the base metal, so itcan fulfill its role as a mold.

In yet another preferred embodiment of this invention, the supportfitting for the heat-resistant block to protect boiler tubes has avertical piece which extends a fixed distance perpendicular from therib, and a catch to engage with the heat-resistant block, which extendsupward from the end of the vertical piece.

The invention is distinguished by the fact that the welding surface ofthe support fitting to the rib is shaped narrower, and a single globuleof a deoxidizing conductive material used as flux is attached to thenarrowed welding surface, and further by the fact that the verticalpiece and the catch engage with each other in double groove style.

With this embodiment, in addition to the effects mentioned above, thesupport fitting is bifurcated to form a groove in the vertical piecewhich engages with a similar groove in the catch. This allows evensupport fittings with complex shapes to be manufactured easily bycombining stainless steel plates, and it allows extremely heavyheat-resistant blocks to be locked securely into place.

In yet another preferred embodiment of this invention, the supportfitting for the heat-resistant block to protect boiler tubes has avertical piece which extends a fixed distance perpendicular from therib, and a catch to engage with the heat-resistant block, which extendsupward from the end of the vertical piece.

The invention is distinguished by the fact that the welding surface ofthe support fitting to the rib is shaped narrower, and a single globuleof a deoxidizing conductive material used as flux is attached to thenarrowed welding surface, and further by the fact that the verticalpiece and the catch are cast from a heat-resistant metal comprising nomore than 0.1% C by weight; no more than 2% Si by weight; no more than2% Mn by weight; no more than 0.045% P by weight; no more than 0.040% Sby weight; from 19.00 to 22.00% Ni by weight; and from 23.00 to 27.00%Cr by weight.

With this embodiment, a cast metal can be used which is produced byminimizing the proportion of C in the existing cast stainless steelSCS18. This will maximize the metal's resistance to corrosion and itswelding capability, and enable it to be formed into complex shapes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) illustrates a support fitting 1 which is related to the firstpreferred embodiment of this invention and is a cross sectional viewshowing the appearance of the support fitting with ferrule 20 in placejust before the arc stud welding using a ferrule begins;

FIG. 1(B) also illustrates the support fitting 1 shown in FIG. 1(A) andis a perspective drawing of ferrule 20 and support fitting 1;

FIG. 2 illustrates a support fitting 1 which is related to the secondpreferred embodiment of this invention and is an exploded perspectivedrawing of the vertical piece and its catch;

FIG. 3(A) illustrates a support fitting 1 which is related to the thirdpreferred embodiment of this invention and is a plain view showing theappearance of the fitting with the ferrule 20 in place just before thearc stud welding begins;

FIG. 3(B) is a side view of the support fitting shown in FIG. 3(A);

FIG. 3(C) is a perspective drawing of the ferrule 20 and the supportfitting 1 shown in FIG. 3(A);

FIGS. 4(A) illustrates the combined structure of boiler tubes andheat-resistant assembly;

FIG. 4(B) is a side view of the combined structure of boiler tubes andheat-resistant assembly shown in FIG. 4(A);

FIG. 5(A) illustrates a vertical cross sectional view of the combinedstructure of boiler tubes and heat-resistant assembly which relates tothe prior art;

FIG. 5(B) is a cross sectional view showing the appearance of thefitting with ferrule 20 in place just before the arc stud weldingbegins; and

FIG. 6 shows the process of the arc stud welding using the ferrule 20according to the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following section we shall give a detailed explanation of theinvention with reference to the drawings. Insofar as the size, shape,relative position of the components, or other features of the componentsdisclosed in these embodiments, they are not intended to limit the scopeof the invention, but serve merely as examples to clarify theexplanation unless otherwise there are specific remarks

FIG. 1 illustrates a support fitting 1 which is related to the firstpreferred embodiment of this invention. At the base of the fitting isthe welding surface. From a rib surface 12 of boiler tube assembly 10,the fitting projects at a right angle from surface 12. On the end of thefitting is a catch which engages with heat-resistant block 16 so thatthe block can be interlocked with the boiler tube assembly. Both theupper and lower corners of the welding surface of the support fitting 1which come in contact with the rib surface 12 are chamfered at a slantto reduce the contact area with the rib surface. A globule of analuminum deoxidizing conductive material 5 used as flux is attached tothe chamfered welding surface 1 a. If the support fitting 1 is aperpendicular piece 4 which extends at a right angle from the rib, theupper surface of the piece 4 is divided into two surfaces. The uppersurface has two different angles, a horizontal surface 4 a nearest thebase where the piece will be welded, and an oblique surface 4 b whichangles upward from surface 4 a. The length of the horizontal surface 4 ais chosen so that the ferrule 20 will fit on it.

Here is a brief explanation of the principle of arc stud welding using aferrule as it would apply to perpendicular piece 4. Ferrule 20 is placedon the end of perpendicular piece 4. The chamfered welding surface 1 aof piece 4 is placed in direct contact with rib surface 12 (the basemetal) with deoxidizing conductive material 5 used as flux between thetwo surfaces. When the welder pulls the trigger of the welding electrode(not shown), a current flows between the piece 4 and the rib surface 12.

The perpendicular piece 4 is automatically withdrawn a given distancefrom rib surface 12 by the lifting mechanism of the welding electrode.An arc is generated inside ferrule 20 between welding surface la ofpiece 4 and rib surface 12. The arc is maintained for a period of timemeasured by a timer. Perpendicular piece 4 and rib surface 12 fuse. Whenthe given period of time has elapsed, the piece 4 is pushed to ribsurface 12, and then the current is cut off.

With this embodiment, then, even if the shape of the support fitting 1is long and narrow, the fact that the welding surface is chamfered makesit easy to achieve uniform contact between that surface and rib surface12 (i.e., the base metal) and enables the welder to achieve a highcontact pressure on the welding surface la. The fact that deoxidizingconductive material 5 used as flux is stuck onto the chamfered weldingsurface la in the form of a globule allows the arc to be started fromthe material 5. This eliminates the possibility for the weld to beuneven.

Because this chamfered welding surface la melts shorter during the studwelding, there is no chance that the chamfered portion will be undercutor have a similar defect. In other words, the corner of perpendicularpiece should be chamfered by predetermined length so that it cannot beundercut during the welding.

Because the welding surface la is shortened by chamfer in this way, themolten metal will not extend very far beyond the periphery of supportfitting 1. This will prevent the ferrule 20 which is placed around thefitting from becoming trapped in the molten metal.

With this embodiment, ferrule 20 is supported by the horizontal surface4 a of perpendicular piece 4 which is at a right angle to the basemetal. Since ferrule 20 is also in rigorous contact with the surface offlat rib 12 (i.e., the base metal) to shield the molten metal, a uniformtemperature can easily be maintained. The ferrule can also fulfill thefunction of a mold.

FIG. 2 relates to the second preferred embodiment of this invention. Inthis embodiment, the support fitting 1 to attach a heat-resistant blockto a boiler tube assembly has a vertical piece 40, which extendsperpendicular to rib surface 12 on boiler tube assembly 10 with awelding surface between the piece and the rib; and a catch 6 for holdingheat-resistant block 16, which extends upward from the front end of thevertical piece.

The upper surface of the perpendicular piece 40 of this embodiment formsa horizontal rectangle. Both the upper and lower corners of the weldingsurface of the piece, the surface which comes in contact with thesurface of the rib 12, are chamfered at a slant to make a chamferedwelding surface 1 a. The deoxidizing conductive material 5 used as fluxis stuck onto the chamfered welding surface la in the form of a globule.Another end of the upper surface of the perpendicular piece 40 has arectangular groove 40 a cut into it which interlocks with a similargroove in catch 6.

Catch 6 is also rectangular. It has a groove 6 a on its lower surfacewhich engages with the groove 40 a on the upper surface of theperpendicular piece 40.

After the perpendicular piece 40 is welded to the rib by arc studwelding using a ferrule, the piece 40 and catch 6 are fitted together byinterlocking their respective grooves 40 a and 6 a.

With this embodiment, the fitting can easily be welded by using an arcstud welding technique. Realizing support fitting 1 as two discretepieces with grooved surfaces which interlock with each other allows evena-fitting with a complicated shape to be manufactured easily from piecesof stainless steel. Such a fitting will secure the attachment of aheat-resistant block 16 which is quite heavy.

FIG. 3 shows a support fitting 1 which relates to the third preferredembodiment of this invention. (A) is a cross section of the fitting withferrule 20 in place just before arc stud welding. (B) is a side view.(C) is a perspective drawing of ferrule 20 and support fitting 1.

The upper surface of the perpendicular piece 40 which comes in contactwith the surface of the rib 12 has the shape of a horizontal rectangle.The upper and lower portions of its welding surface are chamfered toreduce the area to be welded. Deoxidizing conductive material 5 used asflux is stuck onto the chamfered welding surface 1 a in the form of aglobule. Catch 60, a roughly V-shaped tongue on the top of the front endof piece 40, increases in width as it extends upward.

The perpendicular piece 40 and catch 60 may be molded as a single piece.If the piece 40 and the catch 60 are made of a heat-resistant cast metalcomprising no more than 0.1% C by weight; no more than 2% Si by weight;no more than 2% Mn by weight; no more than 0.045% P by weight; no morethan 0.040% S by weight; from 19 to 22% Ni by weight; and from 23 to 27%Cr by weight, they can be welded by arc stud welding without having touse ferrule 20. If this composition were used, percussion stud weldingwould be an appropriate technique.

Arc stud welding using a ferrule differs from percussion stud weldingfor the following reason. In percussion, the chamfered welding surface 1a of perpendicular piece 40 is brought into direct contact with thesurface of rib 12 (i.e., the base metal) with deoxidizing conductivematerial 5 used as flux between the two, however, the welder then pullsthe trigger of the welding electrode (not pictured), and the piece andthe rib 12 can remain in contact until the welding is completed.

In this embodiment, a cast metal is used which is produced by minimizingthe proportion of C in the existing cast stainless steel SCS18. Thismaximizes the metal's resistance to corrosion and its weldingcapability, and enables it to be formed into complex shapes. A supportfitting 1 can thus be made with a shape that is best suited to interlockwith heat-resistant block 16.

As discussed above, with this invention a support fitting can be arcstud-welded using a ferrule easily and reliably without sacrificing anyof its capability. More specifically, this invention allows a supportfitting to be formed which is ideally suited to interlock with aheat-resistant block.

What is claimed is:
 1. A support fitting for a heat-resistant block toprotect boiler tubes, which protrudes upward at a right angle from asurface of a rib provided between two boiler tubes, and which is weldedon the rib, said support fitting comprising: a substantiallyparallelepiped body having a welding surface portion configured to bewelded on the rib and narrowed by chamfering; and a globule flux of adeoxidizing conductive material attached to said welding surface,wherein said substantially parallelepiped body comprises a first portionconfigured to engage with a ferrule for arc stud welding and a secondportion configured to engage with the heat-resistant block.
 2. A supportfitting according to claim 1, further comprising a catch configured tointerlock with said second portion in double groove fashion and engagewith the heat-resistant block.
 3. A support fitting according to claim2, wherein said substantially parallelepiped body and said catch arecast from a heat-resistant metal comprising no more than 0.1% C byweight; no more than 2% Si by weight; no more than 2% Mn by weight; nomore than 0.045% P by weight; no more than 0.040% S by weight; from19.00 to 22.00% Ni by weight; and from 23.00 to 27.00% Cr by weight. 4.A support fitting according to claim 3, wherein said catch comprises asubstantially flat body configured to perpendicularly engage with saidsubstantially parallelepiped body such that the substantially flat bodyis parallel to the rib.
 5. A support fitting according to claim 1,wherein said second portion of the substantially parallelepiped body isslightly angled with respect to the first portion of the substantiallyparallelepiped body.